This invention relates to a method for precise adjustment of an encoder in a brushless motor-encoder combination.
Heretofore, the precision adjustment of an encoder in a directly coupled brushless motor-encoder combination has been carried out according to a flow chart shown in FIG. 6.
In a step 601 of the flow chart, the brushless motor is deenergized, and an encoder disc assembly formed by mounting an encoder disc (rotatable slit plate) on the shaft of the brushless motor is shifted in the shaft direction, so that a gap formed between the disc assembly and a sensor (having semiconductor elements photoelectrically converting light passing through a fixed slit plate and the rotatable slit plate) is thereby adjusted. When the gap is varied by the rotation of the disc, the sensor output waveform deviates. When the adjustment of the gap terminates, the operation is shifted to a step 602. In this step, the motor is energized, and the positions of the light receiving elements of the sensor are adjusted (A-phase elements and A-phase elements are combined into one set, while B-phase elements and B-phase elements are combined into another set. The A phase and B phase are separated by 90.degree., while the A and A phases and B and B phases are both separated by 180.degree., between each other).
The operation is then shifted in a step 603, and the deviation of the surface of the encoder disc in the disc assembly is adjusted while the brushless motor is alternately rotated and stopped several times.
In a step 604, a phase difference .PHI. between an EMF voltage waveform induced across one phase of the motor excitation coils and the output of a specific phase such as the A phase of the encoder is observed. When the phase difference .PHI. is equal to a predetermined value, the operation proceeds to a step 607 wherein the encoder output voltage is adjusted while the motor is rotated. When the output voltage is found to be satisfactory, the operation terminates in a step 608.
However, when it is found in the step 604 that the phase difference .PHI. is deviated from the predetermined value, the motor is stopped and the encoder disc assembly is released from the motor shaft, and displaced therearound so as to correct the phase difference. Such a correction is performed entirely depending on the experience of the operator. The operation is then shifted to a step 606 where the gap is adjusted as in the step 601 while the motor is not rotated. The operation is then returned to the step 603, and the aforementioned routine is repeated until the phase difference .PHI. is made equal to the predetermined value. Upon attaining the predetermined value, the operation proceeds to the step 607.
As described above, in a conventional adjustment of the encoder wherein the phase difference .PHI. between the EMF voltage waveform and the output voltage waveform of a specific phase of the encoder is made equal to a predetermined value, the surface deflection of the disc assembly and the gap between the disc assembly and the sensor are first adjusted before execution of the encoder adjustment, and then the disc assembly thus adjusted is temporarily fixed to the adjusted position, the motor is thereafter rotated, the EMF voltage waveform and the output voltage waveform of a specific phase of the encoder are observed by use of a measuring instrument, the phase relation is thereby confirmed, the motor is stopped, the disc assembly is released, and the angular position of the disc assembly is corrected such that the phase relation is brought into a predetermined condition.
In this case, the surface deflection (parallelism) and the sensor gap are readjusted.
And then the motor is restarted, the phase relation is confirmed again by use of the measuring instrument, and when the predetermined phase relation has not yet been attained, the aforementioned series of operations are repeated.
The above described procedure requires highly skilled labor and an extremely long operation time. Thus mass-production of such a brushless motor-encoder combination is extremely difficult.